The Coalition Agreement is unambiguous: "We will honour our commitment to spend 0.7% of GNI on overseas aid from 2013, and to enshrine this commitment in law". Andrew Mitchell therefore isn't springing a surprise on Conservative whips or backbenchers by pressing for a bill to that effect soon, which today's Daily Mail report could be read to suggest. But some of those who support the commitment to the target will none the less disapprove of the proposal – because it is one thing for a Government to commit itself to a target, and quite another to put it on the statute book.

The core of the case for the latter is that the target is so meritable that such an undertaking is "above party politics", and should therefore be enshrined in law. But the second part of the argument doesn't follow from the first. I support the target (though I'd like to see money directed away from multilateral institutions, a greater share going to child vaccinations, the aid watchdog which has been set up bark louder, the reduction of bureucracy in DFID: in other words, the intensification of the approach which the International Development Secretary is putting into effect).

But I don't favour writing it on to the statute book, because it is usually harmful when matters are placed "beyond party politics". The counter-argument is that a bill would provide opportunities for Parliament to probe whether the commitment is worth making in the first place, give backbenchers a chance to table amendments, provide time for debate, and so on. But this seems to me to be all the wrong way round. Increases or decreases in the target should be straightforward for MPs and peers to effect – enacted by a simple vote in the lobbies, rather than the cumbersome process of repealing or amending the legislation which is now proposed.

Such a measure would also have the effect of making it more difficult for MPs regularly to consider the funding of any commitment, which is a bad thing: the legislature should have more rather than fewer opportunities to hold the executive to account. There is a precedent for the move to which the Coalition is committed. The child poverty target was written into law during the last Parliament, which suggests that what was once unusual is becoming a trend. Matthew Parris suggested in the Times this morning that it may have further to go, contending that the Eurozone crisis may usher in an age of either extremists or technocrats.

In it, he raised an elegant eyebrow at the plethora of bodies that already help separate the Commons from the voters – the Office for Budgetary Responsibility, the Office for National Statistics, agencies, commissions, inquiries by judges, czars, ombudsmen, European conventions. It doesn't follow that we'd be better off were George Osborne to make his own economic forecasts, or were David Cameron to have more control over official statistics. However, Parris is right to suggest that the trend is a dangerous one – "as if reducing child poverty or fuel poverty, or increasing overseas aid, needs to be kept safe from elected politicians", in his words.

But the image of policies being placed "above politics" – secure from where the mucky hands of politicians can grab them, like sweets being placed on a shelf out of the reach of children – is incomplete. Because it is the politicians themselves who are doing the placing – proclaiming their own virtue in the process but, in doing so, simultaneously demonstrating their own weakness.